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. 1984 Sep;76(1):71–74. doi: 10.1104/pp.76.1.71

Inactivation of Glutamine Synthetase by Tabtoxinine-β-lactam 1

Effects of Substrates and pH

Pat L Langston-Unkefer 1,2,3,2, Patrick A Macy 1,2,3, Richard D Durbin 1,2,3
PMCID: PMC1064230  PMID: 16663826

Abstract

The inactivation of glutamine synthetase by tabtoxinine-β-lactam, a phytotoxin produced by Pseudomonas syringae pv. tabaci, was shown to be irreversible. The chloroplast and cytosolic forms of the enzyme from pea leaves (Pisum sativum L.) were separated, purified, and found to be kinetically similar with Km values for glutamate of 6.7 and 4.3 millimolar and for ATP of 2.0 and 1.3 millimolar, respectively. Both forms were irreversibly inactivated by the toxin at equal rates. Using the chloroplast form, it was found that inactivation by tabtoxinine-β-lactam required ATP. Glutamate and low levels of ammonia (<2 millimolar) slowed the rate of inactivation, whereas high levels of ammonia (5, 20, and 50 millimolar) accelerated it. The inactivation proceeded at a faster rate as the pH was increased from pH 6.5 to 7.5. The role which cellular compartmentalization could play in the inactivation is discussed.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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